It is now well recognized that somatic cell hybrids are an important source of specific cellular products that cannot be obtained from short-term primary cultures. The best example of this is the system developed by Milstein and others for the production of hybrid myelomas making monoclonal antibody against an antigen of choice (Kohler and Milstein, 1975, Nature (London) 256:495; Galfre et al., 1977, Nature (London) 266:550). Such hybrids provide a constant supply of monoclonal antibody against specific antigens. These antibodies can be used as reagents for any procedures for which antibodies were previously used, but with the added advantage of higher levels of discrimination, lower background and a continuous available supply of the antibodies.
The production of monoclonal antibodies in general first involves immunization, removal of immune response cells, fusion of these cells, in for example polyethylene glycol, with constantly dividing tumor cells ("immortal") selected for their inability to secrete an immunoglobin. The resulting cells (hybridomas) are distinguished by growth in, for example, HAT (hypoxanthine, aminopterin, thymidine). Each hybridoma is the fusion product of a single-forming antibody cell and a tumor cell having the ability of the former cell to secrete a single species of antibody and the immortality of the latter cell enabling it to proliferate continuously, and provide cell progeny with an unending supply of antibody with a single specificity.